1. Field of the Invention
The invention relates to chemical mechanical polishing (CMP) polisher and more particularly to a slurry mixing apparatus for the CMP polisher.
2. Description of the Related Art
Planarization is an important technology in semiconductor process. The surface of the wafer has an even topography after planarization and it is able to prevent exposure light source from being scattered, so that the pattern transfer can be carried out precisely. Planarization technology mainly includes two methods, spin-on glass (SOG) and chemical mechanical polishing (CMP). SOG can not satisfy gradually the requirement of planarization as the semiconductor technique enters the field of sub-half-micron. CMP is the only process currently that can provide global planarization in very-large scale integration (VLSI) and ultra-large scale integration (ULSI).
CMP is a planarization process to planarize an uneven surface by applying mechanical polishing and adding suitable chemical reagent and slurry. When conditional parameters of process can be controlled appropriately, the planarization degree may reach 94% by CMP. Referring to FIG. 1 and FIG. 2, schematic top view and side view of a CMP polisher known in prior art are shown respectively. A holder 102 holds a backside 106 of a wafer 112, and a front side 120 of the wafer 112 is facing a polish pad 114 on a polish table 100. A slurry 110 from a slurry supplier 118 is pumped into a pipe 104 by a pump 116, and thus, the slurry 110 can be supplied to the polish pad 114 continually. The chemical reagent in the slurry 110 is reacted with the front side 120 of the wafer 112, and the polish table 100 and the holder 102 are rotated along directions 108a, 108b to polish the wafer 112 mechanically by particles in the slurry 110. Chemical reaction and mechanical polishing are repetitively applied on the wafer, and an even surface can be therefore obtained by the planarized process of CMP.
The quality of the slurry determines the stability of the process, so it is important in the planarized process of CMP. Chemical reaction and mechanical polishing are decided by chemical reagent and particles in the slurry respectively. The slurry needs to be diluted by solvent and then can be used, so that the slurry is varied from different materials and it is often necessary to use two kinds of slurry to planarized the wafer.
Since the slurry needs to be diluted to a suitable concentration, a premixer (not shown) is added in the slurry supplier 118 to mix slurry in advance. However, the property of the slurry is easily varied after being mixed. Thus, the slurry has to be consumed after being mixed and before reaching a Pot life. Due to the instability of the mixed slurry, another in-situ slurry mixing apparatus is developed due to the unstable property of the pre-mixed slurry.
Referring to FIG. 3, it shows a side view of an in-situ slurry mixing apparatus in prior art. The in-situ slurry mixing apparatus includes a pipe 202, a pipe 204 (in order to simplify the illustration, only pipes 202, 204 are shown in FIG. 3) and a slurry pipe 206. Different slurries are pumped into the slurry pipe 206 through the direction shown as arrow 202a, 204a from pipes 202, 204. The slurry in the slurry pipe 206 is directly provided onto the polished pad (such as 110 shown in FIG. 2) along the direction of the arrow 206a. However, the mixing time of the in-situ slurry mixing apparatus is too short to cause nonuniformity of the slurry, so that the quality of the slurry can not be easily controlled and result in worse performance of CMP.